Method and apparatus for blasthole stemming

ABSTRACT

A device and process for plugging an explosives blasthole, the device having an inner member (7a, 7b) in the form of a conduit having a valve (9) and being adapted for the passage of fluid bulk explosives and an outer member (1) adapted to engage the walls of the blasthole. The outer member may be made of deformable material or be inflatable. The inner and outer members may be detachable.

This application is the national phase of international applicationPCT/AU96/00690 filed Nov. 1, 1996 which designated the U.S.

The present invention relates to a method and apparatus for use incharging blastholes.

In mining operations the main objective of blasting is to break rock andshift material in a useful way. When an explosive charge explodes thereis a powerful force exerted in all directions and any earth surroundingthe explosive charge will break along the line of least resistance. Inorder to achieve an optimal result in blasting the location and degreeof confinement of an explosive charge must be carefully designed. Inmining applications this generally consists of locating explosivecharges in blastholes drilled in ore, rock, coal or the like. Factorssuch as the diameter, length, angle and spacing of the blastholes arecritical to the success of a blast.

Charging a newly drilled blasthole with explosives generally involvescareful placement of an initiation device such as a detonator, a primerand bulk and/or packaged explosives. Detonators are small, compact highenergy explosives which can initiate a larger body of explosive such asa primer which in turn may detonate with enough force to initiate bulkor packaged explosives. The nature, quantity and arrangement of theinitiation device, primer and bulk or packaged explosives in a blastholehas a large influence on the results of a blast.

Often the blasthole is not completely filled with explosive charges.Often there is a gap between the top of the column of explosive chargeand the collar of the blasthole which is either left open or filled withnon-explosive material called stemming. The column itself may notnecessarily be continuous; sometimes the column comprises severalcharges or short columns separated by inert material or devices referredto as decks are inserted into blastholes to provide discontinuities inthe column of explosive. Decking tends to lower the explosion pressurein a blasthole and provide a more even distribution of energy than canbe achieved in the absence of decking.

In the past many attempts have been made to provide a plugging devicewhich can perform the function of air decking and/or stemming. Forexample attempts have been made to stem blastholes using polymericcontainers filled with water and sealed closed at each end. One end iswell rounded for easy insertion of the containers into the blastholewhere they are secured in place by driving a wedge made of wood orplastic material between the container and the blasthole wall. This typeof stemming is inconvenient to use because of the difficulty of manuallyforcing a water filled container into a blasthole and then driving inwedges while avoiding rupturing the container. These containers areparticularly difficult to place into upholes.

Australian Patent Application No. 41907/93 describes an inflatableplugging device for stemming blastholes. This particular devicecomprises a flexible, inflatable body member which is contained withinan inflexible container. Inflation of the flexible member acts to engagethe walls of a blasthole to keep the device in place and maintainsuspension of the stemming. This device however does not necessarilyeliminate the use of stemming material and it is not always possible fora preformed, inflexible container to conform to the irregular crosssection of a blasthole and thus form a seal.

Blastholes are commonly charged with bulk explosives by pumping orpneumatically conveying the bulk explosive through a loading hose intothe blasthole. One of the drawbacks of most of the plugging devices ofthe prior art is that when such devices are used for decking, it isnecessary to interrupt the charging of the blasthole with explosive inorder to put the plugging device in place. When charging a deepblasthole full of emulsion explosive it is very inconvenient andinefficient to have to cease pumping or pneumatically conveying theemulsion and remove the loading hose in order to insert a pluggingdevice. This method of operation is particularly inconvenient whencharging upholes where the bulk emulsion already in the blasthole startsto slowly flow out of the hole under the influence of gravity before theplugging device is pushed into place.

It has now been found that a plugging device can be provided which canbe placed in position in a blasthole prior to charging and bulkexplosives pumped through the device.

The present invention provides a device for plugging a blasthole whichdevice comprises:

(i) an inner member comprising a conduit for the passage of fluid bulkexplosives material said conduit including a valve means adapted toallow passage of the explosives material in only one direction; and

(ii) an outer member adapted to engage the walls of the blasthole.

The inner member essentially comprises a conduit or passage with anopening or inlet port at one end and an opening or outlet port at theother end through which fluid bulk explosive may be passed. A valveprevents back flow of fluid bulk explosive.

The outer member performs the function of bracing the plugging deviceagainst the walls of a blasthole such that the device forms a good sealwith the blasthole walls and is prevented from slipping out of theblasthole. Clearly it is preferable that the outer member substantiallyconforms to the general shape of the blasthole.

In a preferred embodiment, the outer member is constructed of adeformable material which provides good contact between the device andthe walls of the blasthole. Suitable materials include natural polymericmaterials such as rubber, synthetic polymers such as expandedpolyurethanes or expanded polystyrenes, neoprene and the like.

The outer member may also be inflatable so that the plugging device canbe easily pushed into place along a blasthole and then the outer memberinflated so as to provide good contact with the blasthole walls. Theouter member may be inflated by a source of fluid material locatedexternally such as a cylinder of gas or liquid which is kept underpressure or a reservoir of liquid which may be pumped into the flexiblecontainer. Depending on the fluid used it may be possible to pressurisethe outer member. The flexible container may comprise a filling meanssuch as a non-return valve, bleed valve, needle valve or any otherconvenient means for controlling fluid flow.

The fluid material for inflating the flexible container may be anyconvenient matter and includes liquids, gases or finely dividedparticulate matter. Water and air are particularly inexpensive andconvenient fluid materials.

In a preferred embodiment of the plugging device of the presentinvention the outer member and the inner member comprise separateelements which may be assembled to give the plugging device of thepresent invention.

In such a preferred embodiment, preferably the outer member comprises aflexible container in the shape of cylinder comprising an essentiallytubular conduit or passage along its axis or a flexible container in theshape of a toroid. The outer member may form an inflatable vessel orbag, the surface of which defines a cylinder comprising an essentiallytubular conduit or passage along its axis or an inflatable vessel or bagthe surface of which defines a toroid.

The inner member of such a preferred embodiment of the present inventioncomprises a tube or conduit adapted to be fitted into the essentiallytubular conduit or passage in the outer member and which includes avalve means. Such an inner member may be conveniently referred to as a"liner" as it in effect "lines" the conduit or passage in the outermember when the inner and outer members are assembled to form theplugging device of the present invention.

In a particularly preferred embodiment the liner is tubular in shape andintegral with the valve means. One end of the liner may comprise theinlet port, while the other end of the liner comprises the outlet port.The inlet port may be adapted for attachment of the explosives loadinghose or alternatively the loading hose may be passed through the inletport, part way into the passage or liner.

Preferably the valve means of the device of the present invention islocated at the end of the liner nearest the outlet. The liner may beadapted to allow limited movement of a ball within the sleeve and thusform a ball valve. The movement of the ball may be limited by taperedfins protruding from the inner wall of the liner or a cage or the like.The liner and/or valve means may be constructed of any convenientmaterial such as polymers.

The valve means of the device of the current invention permits fluidbulk explosive to be pumped through the passage of the plugging deviceinto the blasthole but prevents any fluid bulk explosive flow in theopposite direction by sealing off the passage. Where the plugging deviceis being used in upholes, the hydrostatic head should be sufficient tocause the valve to close off the passage.

In general, the plugging device of the current invention is located inplace in a blasthole and fluid bulk explosive is pumped or pneumaticallyconveyed into the blasthole. Initially the bulk explosive passes throughthe plugging device to fill the space between the end of the blastholeand the plugging device. As this happens, air is displaced and it may benecessary to provide means such as a bleed tube by which the air canvent from the blasthole. In a preferred embodiment the device of thecurrent invention is provided with a channel for a bleed tube. It willbe apparent to those skilled in the art that an air bleed tube will notbe required in broken ground or in open holes from which displaced aircan readily escape.

The current invention also provides a method of charging a blastholeusing the device of the current invention. The method comprises thesteps of:

(a) placing initiating explosives and optionally a bleed tube in ablasthole;

(b) inserting the end of an explosive loading hose into the pluggingdevice of the current invention;

(c) locating the plugging device in place in the blasthole;

(d) pumping fluid bulk explosive into the blasthole; and

(e) removing the loading hose.

The plugging device may be pushed into place in the blasthole using theend of the loading hose.

The plugging device of the current invention can be used at any positionwithin a blasthole or for any convenient purpose. For example, theplugging device of the current invention can be used instead of stemmingmaterial or to hold stemming material in place. The stemming device canalso be used in a decked blasthole between charges of explosives orbetween stemming material and explosives charges.

Where the plugging device is used to stem the blasthole the currentinvention provides a further method of charging a blasthole. The methodcomprises the steps of:

(a) placing initiating explosives and optionally a bleed tube in ablasthole;

(b) inserting the end of an explosive loading hose into the pluggingdevice;

(c) locating the plugging device of the current invention in place at ornear the collar of the blasthole;

(d) pumping fluid bulk explosive into the blasthole; and

(e) removing the loading hose.

Where the plugging device of the current invention is used in a deckedblasthole to separate charges of explosives from each other or separateexplosives charges from inert material, the current invention provides afurther method of charging a blasthole. The method comprises the stepsof:

(a) placing initiating explosives and optionally a bleed tube in ablasthole;

(b) part charging the blasthole with explosives composition or inertmaterial;

(c) locating a plugging device of the current invention in place in theblasthole;

(d) repeating step (b) and step (c) until the blasthole is filled.

Commonly in the above method of charging a blasthole the explosivescomposition would be pneumatically conveyed or pumped into the blastholethrough a loading hose but it may be tipped or augered into theblasthole. The inert material may be any suitable non-explosive materialknown in the explosives field such as raw soil, gravel, sand and thelike. The inert material may be charged into the blasthole by anyconvenient means including pneumatic conveying or pumping.

In a preferred embodiment of the above method, the end of an explosivesloading hose or stem material loading hose is inserted into the pluggingdevice of the current invention, the plugging device is located in placein the blasthole and explosives composition or stemming material ispumped through the plugging device.

The method and device of the current invention will now be furtherdescribed with reference to the drawings. FIG. 1 depicts one embodimentof the outer member of the plugging device of the current invention,FIG. 2 is a longitudinal cross section of the liner of the pluggingdevice, dismantled to show its constituent members and FIG. 3 is a crosssection of the assembled plugging device. FIG. 4 depicts the device ofthe current invention in use.

FIG. 1a shows the outward appearance of one embodiment of the outermember (1) of the plugging device which is generally cylindrical inshape and inflatable. The inlet port (2) and outlet port (3) can beclearly seen and are formed from the liner of the outer member. FIG. 1bis a view across the section AA' of FIG. 1a and shows the outlet port(3) and the passage (4) which passes between the inlet and outlet ports.Tapered fins (3a) prevent a ball valve in the liner from escaping fromthe passage. A channel (5) in the outer member (1) provides a conduitfor a bleed tube. FIG. 1c is a view across the section BB' of FIG. 1ashowing the inlet port (2), the passage (4) and the channel (5). Aneedle valve (6) is provided for inflation of the outer member.

FIG. 2 is a cross section of the liner of the plugging device of thecurrent invention, dismantled to show its constituent pieces. The lineris generally tubular in shape, comprising two body members (7a, 7b)which can hold together by interference fit. The inlet port (2) may befitted with an inlet seal (8). A ball (9) fits into the liner near theoutlet port (3). As fluid bulk explosive is pumped along the linertowards the outlet, the ball moves towards the outlet but is preventedfrom escaping the liner by the fins. The bulk explosive flows around theball as the liner near the outlet is of greater diameter than the ball.As the blasthole fills with bulk explosive, the hydrostatic head of bulkexplosive forces the ball away from the outlet, towards the parts of theliner of narrower diameter where the ball lodges, blocking the liner andpreventing back flow of bulk explosive out of the plugging device.

FIG. 3 is a cross section of the assembled plugging device. The two bodymembers of the liner (7a,7b), the ball (9) and inlet seal (8) can beseen located within the outer member (1). An o-ring (10) helps to sealaround the hose used for pumping bulk explosive.

FIG. 4 depicts the plugging device of the current invention in place inan uphole. In practice, after a blasthole is drilled, a detonatorattached to a length of signal tube (12) (or alternatively leg wires) isinserted into a primer (11). The primer is then located in position in ablasthole, preferably using a STOPEPRIME primer locater. (STOPEPRIME isa trade mark of ICI Australia Operations Proprietary Limited.) A bleedtube (14) is then positioned in the blasthole.

Next, a plugging device of the current invention is put in place nearthe collar of the blasthole and the outer member inflated usingcompressed air. Care is taken that the bleed tube passes along thechannel in the outer member of the plugging device. It may be convenient(but not mandatory) that the signal tube also passes along the channel.

The end of an explosive loading hose (13) is inserted into the pluggingdevice and used to push the plugging device into position in theblasthole. Fluid bulk explosive is then pumped through the pluggingdevice into the blasthole. As the blasthole fills with explosiveemulsion, air is displaced from the blasthole and escapes through thebleed tube. By the time the column of bulk explosive has risen from thecollar area of the blasthole to the toe, the hydrostatic head of thecolumn is sufficient to push the ball of the ball valve down and sealoff the passage in the plugging device. The loading hose is subsequentlyremoved and the blasthole is ready for detonation.

The plugging device of the current invention can be used as the solemeans of plugging a blasthole or may be used in conjunction with otherplugging means such as drill cuttings or the like. In some miningapplications it may occur that the blasthole is open at both ends orthat the toe of the blasthole is likely to break through surrounding orinto a fissure, void, old tunnel or the like. In this situation it maybe advisable to locate the plugging device of the current invention atthe toe and the collar of the blasthole.

While the invention has been explained in relation to its preferredembodiments it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

The claims defining the invention are as follows:
 1. A device forplugging a blasthole which device comprises:(i) an inner membercomprising a conduit for the passage of fluid bulk explosives materialsaid conduit including a valve means adapted to allow passage of theexplosives material through the said conduit in only one direction; and(ii) an outer member adapted to engage the walls of the blasthole.
 2. Adevice according to claim 1 wherein the outer member comprises adeformable material.
 3. A device according to claim 1 or claim 2 whereinthe outer member is inflatable.
 4. A device according to any one ofclaims 1 to 3 inclusive wherein the outer member and inner membercomprise separate detachable elements.
 5. A device according to any oneof claims 1 to 4 inclusive wherein the outer member comprises a flexiblecontainer in the shape of a cylinder comprising an essentially tubularconduit along the axis and the inner member comprises a tube adapted tobe fitted into the essentially tubular conduit in the outer member.
 6. Adevice according to any one of claims 1 to 5 inclusive wherein the innermember comprises a ball valve.
 7. A method of charging a blastholecomprising the steps of:(a) placing initiating explosives and optionallya bleed tube in a blasthole; (b) inserting the end of an explosiveloading hose into a plugging device; (c) locating the plugging device inplace in the blasthole; (d) pumping fluid bulk explosive through theinner member conduit into the blasthole; and (e) removing the loadinghose.
 8. A method of charging a blasthole comprising the steps of:(a)placing initiating explosives and optionally a bleed tube in ablasthole; (b) inserting the end of an explosive loading hose into aplugging device; (c) locating the plugging device in place at or nearthe collar of the blasthole; (d) pumping fluid bulk explosive into theblasthole; and (e) removing the loading hose.
 9. A method of charging ablasthole comprising the steps of:(a) placing initiating explosives andoptionally a bleed tube in a blasthole; (b) part charging the blastholewith explosives composition or inert material; (c) locating a pluggingdevice in place in the blasthole; (d) repeating step (b) and step (c)until the blasthole is filled.